Power transducers, such as watt-watthour transducers, are known, and such devices are known to include, for example, voltage and current input scaling means for providing signals proportional to the voltage and current on a power line to be monitored. The signals thus generated are then multiplied by a multiplier circuit to provide an output signal having a value substantially proportional to the power, or rate of energy flow, of the monitored power line.
It has also been heretofore suggested that the multiplier circuit include a pulse width modulating circuit (see, for example, U.S. Pat. No. 3,794,917) wherein one of the input signals (or a signal proportional thereto) is modulated by the other input signal (or a signal proportional thereto) to produce a series of pulses having heights proportional to the instantaneous value of either the current or voltage in the power line and having pulse widths proportional to the instantaneous value of the other. Since the average value of these series of pulses is proportional to the instantaneous power of the power line, filtering and amplification of the modulation output provides an output signal indicative of instantaneous power and integration with respect to time of the modulated output provides an output comparable to total watt hours of energy through the power line for a particular time interval.
Watt/Watthour transducers have also been heretofore suggested to include a comparator receiving a signal from the power line proportional to voltage and the output from a triangle wave generator to produce a pulse width modulated output signal to modulate the signal from the power line proportional to current (see, for example, U.S. Pat. Nos. 3,976,942 and 4,055,804).